Police investigating the 1998 Omagh bombing – the single worst atrocity of the Troubles – have arrested a man in Newry.
The arrest was made on Monday afternoon but police said that there were no further details other than that he had been taken to Antrim Serious Crime Suite for questioning.
A total of 29 nine people, including a woman pregnant with twins, died in the August 1998 blast and a further 200 people were injured in the attack which was claimed by the Real IRA.
No one has ever been successfully convicted of carrying out the bombing in a criminal court.
However, relatives of some victims won a landmark civil action against three suspects held liable for the bomb.
The arrest came on the same day as strong criticism was levelled at former Northern Ireland Secretary Peter Hain after he called for an end to prosecutions for crimes committed before the Good Friday Agreement.
Under his proposal, no one would be pursued for 3,000 unsolved Troubles murders.
The Labour MP told The Times: "This is not going to go away. It's going to continue stalking the First Minister, the Deputy First Minister and the entire body politic there. The past just stalks them and they're either going to confront it and deal with it together or they're going to continue to be stalked by it."
He said the amnesty would apply to soldiers, as well as former republican and loyalist terrorists.